Reduced muscle membrane anion conductance produces hyperexcitability and myotonia. 20,25 Diazocholesterol (20,25 D), an inhibitor of desmosterol-delta 24-reductase, produces myotonia and low GCl in animals which is related to desmosterol accumulation in the surface membrane. The nature of the interactions between membrane lipid phase and anion conductance channels is unknown although a similar pathophysiologic interaction has been proposed in human myotonic dystrophy and myotonia congenita. We will examine the changes in muscle membrane physical, electrical, and chemical properties as a function of temperature and of time after initiation of 20,25 D treatment. We will specifically seek to elucidate the nature of the interaction of the anion channel with the membrane bulk lipid phase under normal conditions and the manner in which this is perturbed in 20,25 D myotonia. New electrophysiological methods will be used in parallel with 35Cl flux measurements, biochemical analyses on isolated sarcolemma, and microviscosity measurements using fluorescence polarization techniques. Variations in membrane parameters as a function of temperature will be examined as a further probe of the relation of channel function to membrane structure in the normal and abnormal state.